Regulating means for gas turbine installations



June 9, 1953 P. FORTESCUE 2,641,324

- REGULATING MEANS FOR GAS TURBINE INSTALLATIONS Filed Aug. 2, 1944 4 Sheets-Sh eet 1 mum/T02 RTE-2, .FOeTESCUE a: mmwm June 1953 P. FORTESCUE I REGULATING MEANS FOR GAS TURBINE INSTALLATIONS Filed Aug. 2, 1944 4-Sheets-Sheet 2 A bo Juhe 9, 1953 Filed Aug. 2, 1944 v P. F ORTESCUE REGULATING MEANS FOR GAS TURBINE INSTALLATIONS 4 Sheets-Sheet I5 IN VE'NTOE R762, Eersscue- 1n eus Patented June 9, 1953 UNITED STATES PATENT: OFFICE REGULATING MEANS FOR GAS TURBINE INSTALLATIONS Peter Fortescue, Bristol, England, assignor to The Bristol Aeroplane Company Limited, Bristol, England, a British company Application August 2, 1944, Serial No. 547,759 In Great BritainFebruary 19, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires February 19, 1963 13 Claims. 1

This invention concerns regulating means for power-plants of the kind in which part of the power obtained from an internal combustion turbine is used to drive a compressor forming a member of said power-plant and the remainder of the power is used externally of the power- ;plant.

Whilst the invention is generally concerned with means for regulating power-plants as above set forth, it has particular reference to means for regulating such power-plants when installed in an aircraft.

It is a characteristic of power-plants of the kind referred to that variations in the operating conditions thereof for example, total power output required, and in the case of aircraft temperature and pressure variations with altitude necessitate adjustments to be made to the power-plant-controls to correct for said variations, since otherwise the eificiencyof the plant may be impaired. When the power-plant isinstalled in an aircraft in which the operating conditions rapidly change and the pilot may be preoccupied with other matters, the power-plant is especially liable to ineflicient operation. It is the adjustment of which ensures that the powerplant functions at a high efiiciency, by performing said adjustments automatically. Moreover by performing certain of the control operations of the power plant automatically, the number. of

controls to which the operator has to attend is reduced.

It is an object of the present invention to provide means for automatically performing certain of the control operations of power-plants -of the kind referred to.

According to the present invention means is provided automatically to regulate a power-plant constant ratio is maintained between the inlet and outlet gas pressures of said turbine.

By the provision of said means it is ensured that within the range of operation for which the power-plant has been designed, there exists a substantially constant expansion ratio through the turbine and that as a result a good turbine .efficiency is obtained throughout said range of .operation.

Moreover when the pressure relationship referred to is maintained, it is found that a direct connection exists between the speed of rotation of the turbine and the temperature of the gases entering the turbine. Advantage is taken oflthis desirable therefore that the operator be relieved of the necessity of attending to those controls of the kind referred to so that a substantially speed-responsive device, and a control which selects the datum setting of the speed-responsive device whereby the quantity of fuel passing to the turbine maintains a selected speed, variations in the latter being rectified by the speed-responsive device adjusting the fuel valve.

A power-plant of the kind referred to may be provided with an internal combustion turbine having a pair of independent rotors through which the products of combustion successively pass, the arrangement being that one of said rotors is adapted to drive the compressor and the other is adapted to provide power for use externally of said power-plant. When an internal combustion turbine of this construction is provided in apower-plant of the kind set forth it is desirable to maintain a preselected speed relationship between the two rotors of said turbine since in this way it is possible to ensure that the power-output turbine operates at or near its optimum efficiency.

According to the present invention therefore a power-plant of the kind aforesaid which incorporates an internal combustion turbine having a pair of independent rotors is adapted to be regulated by, means which automatically maintains a substantially constant ratio between the speeds of the two rotors of the turbine.

It is to be understood that in a power-plant of the kind referred to, in which an internal comfbustion turbine is provided with a pair of independent rotors, said speedand pressure-regulating means may be provided in combination.

To this end, according to another aspect of the invention, means is provided automatically to regulate a power-plant of the kind set forth in which the internal combustion turbine has a pair of independent rotors, said means being adapted -to, ma intain automatically and simultaneously a substantially constant ratio between the speeds of the-pair of rotors and betweenthe inlet and outletgas pressures of said turbine;

I A specific embodiment of the various means .thereinto. passes to the turbin 12 by a series of ducts H 3 which are provided according to the present invention to regulate a power-plant of the kind referred to will now be described with reference to the accompanying drawings of which:

Figure 1 is a diagrammatic illustration of a power-plant of the kind set forth, adapted for installation in an aircraft,

Figure 2 is a schematic drawing of a regulating means which is capable of automatically maintaining the power-plant shown in Figure 1 at a substantially constant ratio between the inlet and outlet gas-pressures of the turbine,

Figure 3 is a diagrammatic illustration of means for varying the datum value of the ratio of the gas-pressures,

Figure 4 is a schematic drawing of a mechanism which, when associated with the regulating means shown in Figure 2, enables the speed of the turbine to be varied by varying the quantity of fuel passing to the turbine,

Figure 5 is a diagrammatic illustration of another form which a power-plant of the kind referred to may take, the turbine being provided with a pair of independent rotors one of which drives the compressor, and the other drives the airscrews of an aircraft in which the plant is installed,

Figure 6 is a schematic drawing showing means for detecting variations in the ratio of the speeds of the pair of rotors or the turbine which forms .air compressors H), II, a turbine 12 which drives the compressors III, II and the variable-pitch airscrews 13, a plurality of combustion chambers 14 through which the air from the compressor passes and in which fuel is burnt, and a duct l5 through which the exhaust gases from the turbine pass and from which they are discharged at [6 in a, direction opposite to the movement of the aircraft. flow type and is placed in series with the cen- The compressor I3 is of the axialtrifugal type of compressor H so as to discharge The air from the compressor ll each of which carries one of the combustion i chambers I4.

'1 the diametral dimensions of the duct i5 and gas-turbine I 2 are less than those of the compressor II and advantage is taken of this to enve-lop the installation as a whole in a streamlined housing 2| whose greatest diameter is that of the compressor H.

The products of combustion pass from each of the ducts H to an annular nozzle-box [8,

through the turbine l2 and into the duct l5.

The turbine I2 drives the compressor H], II and the airscrews I3, each through suitable reduction gearing indicated by the reference I9. I

It will be appreciated that the exhaust gases leaving the duct I5 provide a propulsive thrust to the aircraft. The area through which the discharge gases pass is varied by adjusting the position of a pair of pivotal flaps 20. Adjustment of the discharge throat area varies the power provided by the thrust of the discharging gases and therefore by the airscrews. When the area is small, the thrust of the exhaust gases will be higher (and the thrust from the airscrews correspondingly lower) than when the area is increased.

The present invention provides a regulator means for the power-plant described which will automatically maintain the gas-pressures at the inlet point A to the turbine and at the outlet point B therefrom at a substantially constant ratio.

The means for maintaining the said pressure relationship referred to now be. described with reference to Figure 2.

The inlet pressure to the turbines at the point A (see Figure l) is applied to chamber 22 by a pipe 23, so that variations in said pressure produce expansions or contractions of a stack of evacuated capsules 24 housed within the chamber. Similarly the outlet pressure from the turbine ii at the point B is applied to a chamber 15 by a pipe 26, so that variations in said pressure produce expansions or contractions of a stack of evacuated capsules 27- located within chamber 25. The expansions and contractions of the capsules 24, 2''! are respectively transmitted to a beam 28 by the rods 3d and 3.1. The beam 28 is supported by a link :32 which freely mounted for pivotal movement at 4]. The capsules Z4, 2'! and beam 28 are assembled so that the capsules exert a force at the ends of the beam which maintains it at all times in contact with a roller 5-2 which constitutes a. fulcrumv point for said beam. A bell-crank lever 29 is provided, one arm of which is forked to engage a pin 33 carried by rod 30, whilst the other arm engages the servovalve 34 of a servo-motor 35. The ram '38 of the motor 35 is connected by a linkage, generally indicated at 3}, with the flaps 20 which are provided to vary the throat-area of the discharge nozzle at the rear end of the duct ['5 The motor 35 is operated in. known manner by adjusting the valve 34 endwise in one direction or the otherto permit pressure fluid from the pipe 38 to pass by pipe 39 or 48 to either end of said motor, Whilst the other end is connected to drain by pipes 42 With the arrangement described, whilst the pressures at the points A and B ar in their preselected relationship, the capsules 2d and 21 (which are subjected to these pressures) will maintain the beam 28 in such a position that the Valve 34 is set through the agency of the bellcrank lever 29 to prevent pressure oil passing to the motor 35. Accordingly the flaps 20 are maintained in their existing position. When, however, the pressure at either point A or B varies so that the predetermined relationship is upset, it becomes necessary to adjust the flaps 28 to reestablish said relationship by adjusting the pressure at the point B. When the pressure-variation referred to occurs, it will be transmitted to the chamber 22 or 25, or to both said chambers, depending upon whether the pressure variation occurred at the point A or the point B- or at pendent upon the altitude. :mechanism shown in Figure 3 is provided. This comprises a stack of barometric capsules 43 which are subjected to the pressure of the atmosphere, a -servo-valve 44 which is connected .,with said I capsule 43 by a linkage indicated at 45, a servomotor 46 which is controlled by said valve 44 and a control lever 41 pivotally mounted at 48 :Iandengaging with an arcuate face 49 formed on -the beam 28. metric capsules 43 is varied by the cam 56 whose position is selected by a pilots lever i.

1 In order .to ensure that the control effect pro- "duced by the motor 46 issuflicient exactly. to satisfy the demand made bythe capsules 43 "and/or the cam 50, the servo valve 44 is of the known type comprising a sleeve (not shown) which surrounds the valve and is provided with fbell-crank lever 29 displaces the servo-valve 34 from its normal position and enables the pres- :sure fluid from the pipe 38 to pass to the motor 35. This pressure fluid acts on the. ram 36 to fadjust the setting of the flaps 26'and thereby change the pressure at the point B so as to reestablish the predetermined pressure relationship. When this relationship has been re-established the evacuated capsules 24, 21 will resetthe valve .34 to its normal position, in which pressure v oil from pipe 38 is cut off from the motor 35.

It will be understood that the predetermined pressure relationship referred to may be upset by a change in the pressure at either or both points.

Irrespective of the manner in which the pressure relationship is upset, the change or changes in pressure which result in the ratio of the pressures at A and B being changed, will be trans- .mitted to the capsule stacks in the chambers 22,

'25 and this produces a control effect through the agency of the servo-valve 34 and the servo-motor .35. In the event that the absolute value of the pressures at A and B changes but the ratio remains unaltered, then no control effect will be produced.

It is to be noted that although the beam 28 is "supported by lever 32, the latter being pivotally mounted at 4|, enables the beam freely to turn about the roller 52 The function of the lever 32 is to prevent lateral movement of the beam 28.

It is anticipated that in certain circumstances it may be necessary to vary the datum value of the ratio of the pressures at the points A and B ,in order to ensure that the pivoted flaps 20 (which would otherwise gradually and continuously close the discharge nozzle with the temperature-decrease consequent on an increase in the operating altitude) are biased towards the open position, the amount of this bias being de- The datum setting of the baroports corresponding to those formed by the pipes 153,54. The sleeve is slidable axially and is connected with the motor 46 so that when the latter The free-end of the lever 41 carries the roller 52 (see also Figure 2) which constitutesthe fulc ru m point above-mentioned of thebeam 28.--If therefore the arm is angularlyadjusted to one To this end the the combustion chambers valve is axially adjustable by .a lever 59 which is under the control of a centrifugal governor'fill. The latter is. driventhrough earing 6| fromthe drives the governor. has been operating at a pre-selected speed, increases its speed, this speed-increase is trans- 6 or other side of a central position the roller 52 will move over the surface 49 and as a consequence the ratio of the length of the beam 28 from the point (see Figure 2) to the fulcrum point at 52, and from the point 33 to said fulcrum point, will be changed. Such changes in leverage -necessitate corresponding changes taking place in the forces exerted by the capsules ifthe-beam "28 is normally to assume a position in which the valve 4-4 closes the pipes 39, 40 leading to the motor 35.

When the lever 5 I is moved to adjust the datum setting-of the capsules 43 by the cam 50, the linkage 45 will adjust the servo-valve 44 to permit pressure fluid from the pipe 54 to pass to the motor 46 which thereupon adjusts the position of the arm 41 and hence the position of the 'roller 52. Similarly when the capsules 43 expand or contractwith variations in the operating altitude of the installation, such movements will be transmitted by the linkage'to the servo-valve as already xplained, and as a consequence the position of the roller 52 will be adjusted. In either circumstanca the leverage of capsules 24, 21 is changed and as a consequence the ratio, of the pressures at the points A and B is changed in a corresponding manner. In this way by varying the position of the roller 52 the ratio of the pressures at A and B may be varied as required. When the ratio of the inlet and the outlet gas pressures at A and B is maintained constant in the manner above described there is a direct relationship between the speed of rotationand the temperature of the gases entering the turbine. This temperature depends upon therate late the temperature and speed to ensure that a saf working stress is obtained under all working conditions. This is effected by a simple centrifugal governor driven by the turbine and operating on they fuel valve. Aspecific embodiment of this form of 4 speedtemperature control is shown in Figure 4 in which the fuel from the fuel pump 56 is passed through a metering valve 5'! to a pipe 58 and thence to M. The metering turbine l2. The datum setting of the governor The metering valve 51 is adjusted upon variations in the speed of the centrifugal governor 60 and hence of the speed of the turbine [2 which Thus if the turbine, which mitted to the centrifugal governor 60 andas a result the metering valve 5'! is adjusted to reduce the quantity of fuel passing to the turbine. The

speed of the latter is therefore reduced until it again operates at the pre-selected speed. Similarly if the speedlof the turbine falls the centrifugal governor 60 adjusts the valve 51 to increase the quantity of fuel, thereby returning the turbine to its preselected speed value.

In vorder to varythe speed of the turbine 12 ment of the metering valve 51 so as to select a quanti iyfiof; fuel for "the :turbine operation such tha sa dtu hineota es t he peed sele t d- When such a datum speedhas been selected and obtained, the centrifugal governor will maintain t e r i e at hat sp ed va ue by adi stins t setting of the metering valve.

- The power-plant shown in Figure 5 is of similar general construction to that of Figure 1. It eompr-ises an axial-flow type of compressor 10 a c nt f l t p of comp sor .1 I into which com pressor l discharges, a. turbine [2 which drives the compressors I0, II and the variable pitchairscrews I3, a plurality of combustion chambers 14 through which the air from the compressor passes and in which fuel is burnt, and a duct l5 through which the exhaust gases from the turbine pass to be discharged at It, With a view to pre-heatmg the air which passes from the compressors 18, ll to the combustion chambers M, a heat-exchanger ,6] is provided. The latter is disposed in the duct 5 s hat the ex aust ga es pass through t e heat-ex er as thev m theurb ne 12 to the disharge orifice at 1.6. The air from the compresor l l passes to the heat-exchanger [.6 by a series of ducts 65, Whilst the heated .air from the heat-exchanger passes to the turbine by a plurality of ducts '66 .each of which carries one of the combustion chambers I4. The ducts 6.5, 66 lie around the periphery of theduct 1.5 which has smaller-diametral dimensions than the compressor ll due to the similarly smaller dimensions of the turbine I2 and heat-exchanger .64. In this way the ducts 65, .66 do not extend radially beyond the periphery of the compressor. The-ducts 6.5 56 are intercalated.

In order to provide a power-plant ofgreater flexibility in operation than the plant shown ';in Figure 1, the turbine 12 of the power-plant. shown in Figure 5 is provided with a .pair of independent rotors ,61, 68. The products of combustion pass from the combustion chambers IA to an annular fnozzle'box 69 and then in succession through rotor 61, nozzle box in (which issandwiched between the two rotors) and therotor 6 8. Y'Ihe rotor 61 is coupled to the compressors 110, H vas at "H, driving it, if desired, through a reduction gearing. The rotor 68 drives the airscrews .l3tl 1Q l h a suitable reduction gearing (not shown) located between the compressor [D and saidairscrewsefor instance within housing 12.

The power-plant is. enclosed in. a streamlined housing 2.1.

The exhaust gasesjfrom the turbine which are discharged at 16 provide a propulsive thrust to the aircraft. The area of the or fice ihrough which the gases at it pass varied'by adjusting I the position of the pivotal flaps .20.

In a power-plantas described with'referenceto Figure 5 it isnecessary to ensure that the speed of the rotor 58 is proportional to the velocity of the gases leaving the nozzle box if said rotor isto operate in an eiiiicient manner. It can be shown that this velocity is proportional to the speed of the compressor l0, l1 and hence .of the rotor. 68 will be met. The pilot is therefore relieved of this duty. The mechanism which is provided tomaintain said s i ed relationship is shown in Figures Band 7.

In'Fjigure *7 a'blade "13 of the airscrews i3 is shown as connected for pitch-variation 'to the ram '14 of -a hydraulic motor '15. The admission and discharge of pressure oil to and from the 'motor '15 is regulated by a valve 15. "The latter normallyassumes a central position (as =willbe 1 8 described eme-1a.fiel in wh h pre sure oil i re nted t cm in o. t am. said me Hwe er, val 6 is ca abl 9 axial m em nt o a s e e thc 'oi t o Po ion in each of h ch e P e su e ,11 is rm t d to Pa s to the me 225- In o s c p s t on the ot r 5 will e? brought into, operation to move the airscrew b ade to oa n itch and in th t e 1 tion the motor will move the blades to a finer p h pos n- To effect hes ch-change movements a um d s l rom a fifi YQ r 18 and Pass s i to e m or b a p e 1 and either pipe 19 or depending upon the position which valve '16 assumes. The fluid discharged from the motor 15 passesby Pipe 8;) or 19 through the interior of. the valve and n b p pe .8? to the reservoir 18. These parts 15, H, Island 88 are outside the hub being suitably carried by plant structure and the drive to pump 88 is taken from the compressor to as'here'inatter described.

Whilst t e ratio of the speeds of the roiii is .51. 6B is maintained constant the. valve 1.5 assumes a central position in which the pipes l9 and 8.0 are closed respectively by the lands .83, B4 of theusaid valve. Under these conditions the pressure 011 from pump l! is incapable of passing to the mo.- tor 15 to efiect any change inpitch. The .oil delivered by pump ll is then circulated around the branch pipe .85 and relie irvalve.

When the speed-ratio between the rollers is upset, the speed of rotor, 68 (which drives the airscrews i3) is automatically adjusted .bych-anging the pitch of the airscrews .so as tore-establish said ratio.

Wi h this end in .view the valve It capable of being displaced axially one way or the other,

he by n n th pr ss r -ai ow Pump 1- to pass to the motor '15 to effect the required pitch-change movement. For this purpqse each endof the valve 16 is connected by api sfi, 8,1 with a sear-type pump B8. When the 111 1 8 8 delivers oil under pressure tothe pipe-i3] .theyalve 35 will .be moved towards .the lett and the pump 11 will pass pressure oilto :motor 715 by pipe J9. Consequently the ram "14 will be moved towards the right to effect a,pitchechange.movement'in ione sense thereby altering the :speed of rotor 16 to re.-esta blish the speed-ratio relationship between the rotors. Simultaneously oil passes'from thezcther side of motor E5 to th reservoir laby pipes 80, 82. "Similarly when pump 88 delivers pressure oil'to pipe '8B va1ve *lBistnoved tothe right and assumes the positionshown injFigure 7 in hic oi nde n es ur f om. pump 7' asse y n n t mete 15 nd h 'am 1. i

moved towards the'lefli 12 ef ect a Ditch-change movement in the .QDPoSitesense. This has the thereservoiy'lfi bypipe 90.

The pump 8581s capableaof rotation both. clockwise and antieclockwise, the arrangement being that when'it rotates in one direction-it will deliver topipe 'BGand when itrotates in the opposite direction it-will deliver to pipe 87. As will be appreciated of course whilst the pumpis inoperative cate the-valve in said position-whilst-the pump 88 is inoperative.

The pump 88 is driven by the differential speed unit shown in Figure 6. This comprises a pair of coaxial bevel gears 9|, 92 of which gear 9| is driven from the airscrew-shaft 93 through a mon axis of the bevel gears 9|, 92 and is connected through a suitable gear train indicated at I 02 with the pump 88.

So long as a predetermined speed relationship is maintained between the turbine rotors 61 and 68 the bevel gears 9|, 92 will be rotated at the same speed in opposite directions and accordingly the planet-carrier I08 will be maintained stationary. If the speed of either of the turbine rotors 6! and 68 assumes a value which upsets the predetermined speed relationship the I co-axial gears 9|, 92 rotate at diiferent speeds and the planet carrier I will in consequence commence to rotate about support I 9| thereby I3 and turbine rotor 68 is altered to restorethe speed relationship between the rotors 61, 68 which it is desired to maintain.

The speed-control mechanism described with reference to Figure 6 may be replaced by other .forms of mechanism which are capable of detecting differences from a preselected value of the ratio between the speed of the turbine rotors 61, 68 and of re-establishing the pre-selected value upon a difference being detected. Thus an electric differential unit may be provided, which receives current from a pair of alternators, one being driven at a speed proportional to that of the rotor 6'! and the other at the speed of the rotor 68. The differential unit is responsive to frequency diiferences which are produced T when the speed of the airscrews or compressor alters and upsets the pre-selected value of speed ratio. The difierential unit suitably adjusts the valve 16 thereby altering the pitch of the airscrews I 3 to bring about a return of the preselected ratio of the speeds. It will be appreciated that the power-plant described with reference to Figure is capable of ,being regulated so as to maintain a constant ratio between the inlet and outlet gas pressures of the two-stage turbine [2. This pressure regulation is preferably performed in a similar manner to that described as being provided for the regulation of the power-plant of Figure 1. It is used, however, in association with the speedratio regulation which has been described as being provided for the regulation ofthe powerplant of Figure 5.

I claim:

1. A power plant comprising a gas turbine having a pair of independent rotors through which the working fluid passes in series, a combustion chamber for producing the working-fluid for the gas turbine, an air compressor driven by one rotor of the gas turbine and supplying combustion air to said combustion chamber, power absorbing means external of the power plant 'driven by the other rotor of the gas turbine,

means responsive to the speed of each rotor, and control means actuated by said speed responsive 1 means automatically to maintain the ratio between said speeds substantially constant with variations in said speeds due to changes in the operating conditions of the power plant.

2. A power plant comprising a. gas turbine having a pair of independent rotors through which working fluid passes in series, acombustion chamber for producing the working fluid for the gas turbine, an air compressor driven by one rotor of the gas turbine and supplying combustion air to said combustion chamber, power absorbing means external of the power plant driven by the other rotor of the gas turbine, means responsive to the pressure .of the working fluid at the inlet to the turbine and at the outlet therefrom, control means actuated by said pressure responsive means automatically to maintain the ratio between said pressures substantially constant, means responsive to the speed of each rotor and control means actuated by said speed responsive means automatically to maintain the ratio between said speeds substantially constant.

3. A power plant comprising a gas turbine having a pair of independent rotors through which the working fluid passes in series, a combustion chamber for producing the. working fluid for the gas turbine, an air compressor driven by one rotor of the gas turbine and supplying combustion air to said combustion chamber, power absorbing means external of the power plant driven by the other rotor of the gas turbinemmeans responsiveto the speed of each rotor and control means actuated by said speed responsive means to vary the power absorbed by said means external of the power plant to maintain automatically the ratio between said speeds substantially constant with variations in said speeds due to changes in the operating conditions of the power plant.

4. A power plant for a propeller-driven aircraft comprising a gas turbine having a pair of independent rotors through which the working fluid passes in series, a combustion chamber for producing the working fluid for the gas turbine, an air compressor driven by one rotor of the gas turbine and supplying combustion air to said combustion chamber, a variable-pitch propeller producing the working fluid for the gas turbine,

an air compressor driven by one rotor of the gas turbine and supplying combustion air'to said combustion chamber, a hydraulically operated variable-pitch propeller driven by the other rotor of the turbine, a difierential speed unit one :member of which is driven at the speed of one rotor and another member or which is driven at the speed of the other rotor, a hydraulic pump driven by the diflerential speed unit and valve means actuated by the pressure fluid delivered by said pump, said valve means regulating the admission and discharge of pressure fluid to and from the hydraulic pitch-change mechanism of the propeller.

combustion air to said combustion chamber,

power absorbing means external of the power plant driven by the other rotor of the gas turbine, a pressure responsive device subjected to the pressure of the working fluid at the inlet to the first turbine rotor, a further pressure responsive device subjected to the pressure of the working fluid at the outlet from the second turbine rotor, a beam to which each of said devices is coupled, a servo-valve actuated by said beam, a hydraulic servo-motor the admission and discharge of pressure fluid to and from which is regulated by said valve and means operated by said servo-motor for varying the area of an orifice through which the gases from said second turbine rotor are discharged.

'7. A power plant comprising a gas turbine having a pair of independent rotors through which the working fluid passes in series, a combustion chamber for producing the working fluid for the gas turbine, an air compressor drivenby one rotor of the gas turbine and supplying com bustion air to said combustion chamber, power "absorbing means external oi the power plant driven by the other rotor of the gas turbine, a pressure responsive device subjected to the pressure of the working fluid at the inlet to the first turbine rotor, a further pressure responsive device subjected to the pressure of the working fluid at the outlet from the second turbine rotor, a beam to which each of said devices is coupled, a servo-valve actuated by said beam, a hydraulic servo-motor the admission and discharge of pressure fluid to and from which is regulated by said valve, means for varying the fulcrum point of the beam to vary the relative control effects of the pressure responsive devices on the beam and hence on the servo-valve and means operated by said servo-motor 'for varying the area of an orifice through which "the gases from said second turbine rotor are discharged.

8. A power plant for an aircraft comprising a gas turbine having a pair of independent rotors through which the working fluid passes in series, a combustion chamber for producing the working fluid for the gas turbine, an air compressor driven by one rotor of the gas turbine and supplying combustion air to said combustion chamher, power absorbing means external of the power plant driven by the other rotor of the gas turbine, at pressure responsive device subjected to the pressure of the working fluid at the inlet to the first turbine rotor, a further pressure responsi-ve device subjected to the pressure of the working fluid at the outlet from the second tur- .bin:e.rotor, a beam to each of said devices is coupled, a servo-valve actuated by said beam,

"a hydraulic servo-motor the admission and discharge :of pressure fluid to and from which .is regulated by said valve, a barometric capsule connected with the :fulcrum point of said beam automatically to vary the relative control effects of the pressure responsive devices with variations in the operating altitude of the aircraft, a manual control for varying the datum setting of said barometric capsule and means operated by said servo-motor for varying the area of an orifice through which the gases from said second turbine rotor are discharged.

9. A power plant comprising a gas turbine having a pair of independent rotors through which the working fluid passes in series, a combustion chamber for producing the Working fluid for the gas turbine, an air compressor driven by one rotor of the gas turbine and supplying combustion air to said combustion chamber, power absorbing means external of the power plant driven by the other rotor of the gas turbine, means responsive to the pressure of the working fluid at the inlet to the .first turbine rotor and at the outlet from the second turbine rotor, control means actuated by said pressure responsive means auomatically to maintain the ratio between said pressures substantially constant, a fuel-supply valve for regulating the quantity of fuel supplied to the combustion chamber and means responsive to the speed of one of the rotors of the turbine for adjusting said fuel-supply valve.

10. A power plant comprising a gas turbine having a pair of independent rotors through which working fluid passes in series, a combustion chamber for producing the working fluid for the gas turbine, an air compressor driven by one rotor of the gas turbine and supplying combustion air to said combustion chamber, power absorbing means external of the power plant driven by the other rotor of the gas turbine, means responsive to the pressure of the working fluid at the inlet to the turbine and at the outlet therefrom, control means actuated by said pressure responsive means automatically to maintain the ratio between said pressures substantially constant, means responsive to the speed of each rotor, control means actuated by a said speed responsive means automatically to maintain the ratio between said speeds substantically constant, a fuel-supply valve for regulating the quantity of fuel supplied to the combustion chamber and means responsive to the speed of one of the rotors oi the turbine "for adjusting said fuel-supply valve. 11. A power plant as claimed in claim wherein the speed responsive means is a flyweight governor driven by one of the rotors of the gas turbine, said governor being adjustable by a manual control to vary the datiun speed of one of said gas'tur'bine rotors.

12. A power plant comprising a gas turbine having apair of independent rotors through which the working fluid passes .in series, a combustion chamber for producing the working fluid for the gas turbine, an air-compressor driven by one rotor of the :gas turbine and supplying combustion air to said combustion chamber, power absorbing means external of the power plant driven by the other rotor of the gas turbine, means responsive to the speed of each rotor and control means actuated by said speed responsive means automatically to maintain a predetermined relationship between said speeds. 13. A power plant comprising a gas turbine having a pair of independent rotors through which the working fluid passes in series, a combustion chamber'ior producing the working fluid for the gas turbine, an air compressor driven by 13 one rotor of the gas turbine and supplying combustion air to said combustion chamber, power absorbing means external of the power plant driven by the other rotor of the gas turbine, means responsive to the speed of each rotor, control means actuated by said speed responsive means automatically to maintain the ratio between said speeds substantially constant with variations in said speeds due to changes in the operating conditions of the power plant and regulating means for selecting said ratio at will.

PEIER FORTESCUE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 23,198 Anxionnaz Feb. 21, 1950 872,377 Samuelson Dec. 3, 1907 993,982 I-Ialliwell May 30, 1911 1,809,271 Goddard June 9, 1931 2,026,814 Caldwell et a1 Jan. 7, 1936 2,050,349 Lysholm et a1 Aug. 11, 1936 2,105,089 Martin Jan. 11, 1938 2,160,281 Price May 30, 1939 2,162,956 Lysholm June 20, 1939 2,173,913 Morehouse Sept. 26, 1939 Number Number 2 5 9 1,848 495,469

14 Name Date Waseige Apr. 1, 1941 Martin Oct. 28, 1941 Mercier Mar. 17, 1942 Lysholm Apr. 28, 1942 Goddard June 16, 1942 Pescara Aug. 4, 1942 Jendrassik Dec. 15, 1942 Jung Dec. 29, 1942 Anxionnaz Aug. 22, 1944 Lysholm Sept. 26, 1944 Heppner Oct. 10, 1944 Blanchard et a1. Nov. 14, 1944 Anxionnaz Mar. 19, 1946 Larrecq Apr. 23, 1946 Heppner July 23, 1946 Pavlecka et a1 Oct. 15, 1946 Martin June 3, 1947 McCoy Dec. 7, 1948 Griflith Aug. 2, 1949 Price July 11, 1950' FOREIGN PATENTS Country Date Sweden Mar. 26, 1938 Great Britain Feb. 8, 1937 

